Summary

Students use the spectrograph from the "Building a Fancy Spectrograph" activity to gather data about different light sources. Using the data, they make comparisons between the light sources and make conjectures about the composition of these sources.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Spectrographs are used both in ground- and space-based telescopes to help astronomers figure out the materials that make up stars, planets, and planetary atmospheres. Mechanical and electrical engineers build these spectrographs to advance our knowledge of astronomy. The engineering of a spectrograph determines what kind of light it can analyze. For example, the materials involved affect what can be seen through the spectrograph and whether spectral lines can be seen or "resolved" at all.

Pre-Req Knowledge

Students should have completed the "Building a Fancy Spectrograph" activity and its homework assignment before completing this one. Students should have some understanding of the nature of light, (such as, rainbows are formed with light, light can be different colors, light can be obscured by physical objects, burning creates light, etc.).

Learning Objectives

After this activity, students should be able to:

Use a spectograph to gather data about different light sources.

Describe that light seen through a diffraction grating shows all of the component colors of that light.

Describe how engineers may redesign an spectrograph based on what the spectrograph is being used to examine.

More Curriculum Like This

A Spectral Mystery

Students use the spectrographs from the "Building a Fancy Spectrograph" activity to gather data about light sources. Using their data, they make comparisons between different light sources and make conjectures about the composition of a mystery light source.

Students create and decorate their own spectrographs using simple materials and holographic diffraction gratings. A holographic diffraction grating acts like a prism, showing the visual components of light.

Students find and calculate the angle that light is transmitted through a holographic diffraction grating using trigonometry. After finding this angle, student teams design and build their own spectrographs, researching and designing a ground- or space-based mission using their creation.

Students learn how using spectrographs helps people understand the composition of light sources. Using simple materials including holographic diffraction gratings, students create and customize their own spectrographs—just like engineers.

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;
within type by subtype, then by grade, etc.

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Glow sticks can be purchased at big box stores, camping supply stores, and many grocery stores, and are especially easy to find around Halloween. Glow sticks range in price from $1-$4 each. Make sure to get the kind that needs to be cracked to glow.

The ¼ watt night-lights (sometimes called 0.25 or 0.3 watt) can be purchased at hardware stores, many grocery stores, and some big box stores, and typically less than $5 each.

Introduction/Motivation

Astronomers use spectrographs to figure out of what materials the atmospheres of planets, moons, and other objects in the Solar System are made. Using the spectrographs that you built, we are going to look at some different light sources. We will gather information about these light sources and figure out how astronomers determine what an atmosphere is made of.

Think about your spectrograph. There are many factors that went into the design of this spectrograph, even though it is a simple one. Engineers must consider all aspects of a design, from the length of the spectrograph to the angles present in the spectrograph. Often, they use computer modeling to help them design better instruments, but they also brainstorm with other engineers or read papers that engineers have written to help them come up with better ideas. Take some time to think about the components of your spectrograph, and we will discuss the strengths and limitations of our spectrographs before we begin.

Vocabulary/Definitions

absorption spectrum: Dark lines that appear against the continuous spectrum seen through a spectrograph.

continuous spectrum: The rainbow that white light is composed in which each color is equally bright.

diffraction: When light bends around an obstacle or through a small opening like those in a diffraction grating.

spectrograph: A tool that allows the components of light to be seen easily with the eye. (also spectroscope)

spectrum: The pattern light produces when passed through a prism or diffraction grating, as seen through a spectrograph. (plural: spectra)

Procedure

Terminology Note

In creating the Spectroscopy curricular unit, the Project SPECTRA! program chose to use the term “spectrograph” (as opposed to spectroscope) for the engineering projects activities because a spectrograph is a tool used in spacecraft and modern telescopes, and Project SPECTRA! is an astronomy program. A spectrograph uses a detector, usually a CCD (a charge coupled device, similar to those used in digital cameras), to record the properties of light. Technically, in this unit, students build “spectroscopes,“ which are similar to spectrographs, however, instead of using a detector, the human eye directly observes the light within the scope or projected onto a screen. The primary difference between the two instruments is the method in which the light is detected. A spectrograph enables a person to observe light that cannot be seen with the eye (typically ultraviolet, infrared, and x-rays) because the detector records these wavelengths electronically, enabling the signals to be observed as plots or graphs. In this curricula, when students build their “space-worthy” spectrographs, we consider the students themselves to be the detectors, and leave to their instructors the option of providing students with more in-depth explanation.

Below are examples of the types of spectra you can see with different lights:

Florescent light bulbs contain mercury vapor inside and a phosphorescent coating on the glass. The bright lines are from the vapor, and the continuous spectrum is from the phosphor. Depending on the quality of the bulb, one may or may not be able to see the continuous spectrum. If the bulb is very high quality, the continuous spectrum may be all that you can see. A lower quality bulb only produces a line spectrum.

A candle (seen at a distance) produces a continuous spectrum.

Incandescent bulbs and holiday lights produce a continuous spectrum.

Glow or light sticks produce an emission spectrum that depends on the type of dye inside. A chemical reaction causes the atoms in the dye to become excited and release photons. Even if the packaging says "neon" it is not actually neon gas that fills the tube, and the spectrum will not match that of a neon source. Students may have difficulty centering the light in the slit and must hold the glow stick steady several inches from the slit to observe the spectrum. It needs to be fairly dark to observe the spectrum.

A ¼ watt night light with a neon bulb produces a neon emission spectrum. If the night light is the "jewel" type, it will not produce a clear spectrum so the casing must be removed and the connections covered with electrical tape (before plugging it in). It is preferable to get one that is not a "jewel" style, as it is difficult to remove a casing, and removal of the casing poses the risk of shock. It needs to be fairly dark to see the spectrum, and students may have to adjust their distance to the light while maintaining the light in the slit.

Before the Activity

Have students build a simple spectrograph, using the associated "Building a Fancy Spectrograph" activity.

Set up light sources around the room, making sure that there is distance between each source.

Make copies of the student worksheet.

Review homework from "Building a Fancy Spectrograph."

Turn off lights.

With the Students

Tell students that their job as engineers today is to establish what makes up all of the light sources that are around the room using the spectrographs they built in the "Building a Fancy Spectrograph" activity.

Have students rotate though the stations, spending about 5 minutes at each different light source.

Using their worksheets and homework from "Building a Fancy Spectrograph," have students describe and draw the spectra of the various light sources around the room.

During the activity, walk around the room and ask students questions pertaining to the spectra they have drawn. Whenever possible, see if students used the same light sources from today's activity in the homework for "Building a Fancy Spectrograph" and help them draw comparisons between their homework drawings and their drawings during today's activity.

Provided below is a suggested order to show students the different types of light. This order provides a gradual progression from a typical full-spectrum light bulb to many different types of spectrums.

Incandescent Light: Start with the incandescent light bulb to make sure everyone's spectroscopes are working properly. Students should see a full continuous color spectrum. All colors should be equally bright with no breaks in the spectrum. Have students draw the spectrum they see. Mention that this type of light is the same as what you would see from natural sunlight.

Cool White Compact Florescent Light (CWCFL): Explain that this next type of light is called, "compact florescent light" (bulbs called CFLs), which are the bulbs that last longer and use less energy. For the CWCFL, light is emitted throughout the spectrum. Ask students how this looks different from the incandescent light. What has changed? (Instead of all colors being equally bright, some color bands are brighter than others). Explain that breaks (black bands) in the spectrum indicate the light source is not emitting light waves in that section of the spectrum. Have them draw the spectrum.

Soft White Compact Florescent Light (SWCFL) and Cool White Compact Florescent Light (CWCFL): Explain to students that the next two types of lights are still compact florescents, however, one emits stronger from the blue/purple (cool) side of the spectrum while the other emits stronger from the red (warm) side of the spectrum. Put one in and ask them to guess which one it is.

- SWCFL: Expect students to realize that the light emitting from this bulb is tinted red, so they might get the hint that something should look different on the red side of the spectrum. Ask students which one they think it is. If they are not getting it, explain how little or no breaks exist along the red side of the spectrum whereas huge breaks exist between purple and blue. Have them draw the spectrum.

- CWCFL: Similar to above, expect students to realize this light, to the naked eye, looks very blue compared to the other lights they have looked at. Ask them how this characteristic is reflected in the spectrum they see through the spectroscope. How does this spectrum looks different? (The spectrum emits more from the blue/purple side. The purple and blue bands are much thicker here than on the SWCFL and there are breaks in the red side.) Have them draw the spectrum.

Red Compact Florescent Light (RCFL): Show students the RCFL before lighting it. Ask them what they think they'll see (some may say just red, some may say all colors, some might say mostly red). Then light the bulb and let students look at the spectrum. Ask them: 1) Do you see only red? (No. Some might say yes, but ask them to look closely); 2) What other colors do you see? (A thin green band and a thin yellow line); and 3) Does that surprise you that part of this light is made out of green and yellow light? Have them draw the spectrum.

Blacklight Compact Florescent Light (BCFL): Screw in the BCFL. Ask students: 1) What do you see? (Very thick black bands/breaks in the spectrum); 2) Which bands are the brightest? (purple, blue, green); 3) Is this a bright light to the naked eye? (No.); 4) If you only looked at this through your spectroscope, could you predict this would be a dull light to the naked eye? How? (Many sections of the spectrum do not emit light.) Have them draw the spectrum.

Red LED and Green LED: LED lights are not that bright, so students need to get close to the light source to see the spectrum. One way to do this is to buy LED nightlights and plug in a few of different colors around the room so students can roam and look at each. After they have looked at both, ask students: 1) What did you see with the red LED? (Only red); 2) Was the red LED spectrum bright? (No); 3)What did you see with the green LED? (Mostly green, maybe a little yellow); 4) Was the green LED spectrum bright? (No) and 5) Were either of these lights bright? (No) Have them draw both spectrums.

Attachments

Safety Issues

Make students aware of fire safety as it pertains to the use of candles.

Troubleshooting Tips

Colorblind and vision-impaired children will have difficulty with this activity. Students with corrective lenses will not have difficulty. Pair colorblind students with another student to assist with the activity and homework.

Students may need assistance adjusting the position of the diffraction grating so that a spectrum appears in their spectrographs. The lid must be rotated if a spectrum is not visible.

Make sure all light sources have been tested prior to the activity to confirm that they are operational. It may be beneficial to have extra light sources in case one fails to operate.

Assessment

Pre-Lesson Assessment

Accessing Prior Knowledge: Review homework from "Building a Fancy Spectrograph" and ask students questions pertaining to the light sources they drew. Ask them to make comparisons between their light sources and their neighbor's light sources. Have them share their findings with the class. Highlight key concepts on the board based on their discussion.

Activity Embedded Assessment

Class Discussion: Ask students what astronomers might gain from understanding the atmospheres of other planets. Reinforce the idea that without engineering technology such as spectrographs, scientists would be unable to determine what a planetary atmosphere contains. Ask students to brainstorm about the limitations and advantages of the spectrographs that they built.

Worksheet: Have students complete the activity worksheet; review their answers to gauge their mastery of the subject matter.

Post-Activity Assessment

Class Discussion: At activity end, students should be able to explain that light sources produce a specific pattern, and that the pattern does not change. Continuing the discussion period after the lesson is crucial. At the end of the unit, students should understand that the spectrum of a light source is different depending on what the light source is made out of, that sources that have an identical spectrum have an identical composition, and that gasses have a specific composition that can be seen by passing electricity through them or through a chemical reaction to produce light. Students can then better understand how engineers help astronomers gather information about what a body is composed of by examining light, and links can be made between this activity and astrophysical data about the compositions of planetary atmospheres.

Contributors

Copyright

Supporting Program

Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education, and National Science Foundation GK-12 grant no 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.